1. Field of the Invention
The invention presented here lies in the field of the designing of addendum zones of tools for the manufacture of formed sheet metal parts (deep-drawing/stretch-forming processes) and their optimization.
2. Discussion of Related Art
Formed sheet metal parts as a rule are manufactured by deep-drawing. The semi-finished parts, the so-called sheet metal blanks (blank), for this purpose are placed in multi-part forming tools. By means of presses, in which the forming tools are clamped, the parts are formed. The parts, as a rule, are manufactured out of a flat sheet metal blank in several forming steps (drawing, reshaping, setting, etc.), combined with trimming steps. In this process the edge areas, in particular the addendums, represent problematic zones. In the designing of the tools for a forming step the concern is, among others, to complement the correspondingly prepared component geometry. In the case of multi-step processes, intermediate geometry (component geometry and intermediate geometry both being hereinafter referred to as component geometry) in the edge zones is modified by an addendum such that, from it, a tool geometry is produced with which the predefined component geometry can be manufactured such that no failure occurs (cracks and wrinkles) and that other quality requirements, for example, a limited reduction of the thickness, the achievement of a minimum stretching of the sheet metal, and manufacturing technology restrictions are adhered to.
The dimensioning and adjustment of the addendums represents a great problem field today. Not infrequently several months elapse, until a tool works satisfactorily. Frequently, this is an iterative process, which is associated with a lot of rejected parts and a substantial consumption of energy and other utilities. The production of addendums today, to a great extent, takes place manually by means of computer-aided design systems (CAD) and takes a lot of time. In doing so, frequently hundreds of individual surfaces are created and edited by the designing of curves, supporting surfaces derived from them, and their trimming. Already solely the establishment of an addendum for a large body part can, as a result, easily take several weeks. This procedure also calls for a great specialist knowledge in the fields of forming technology and CAD of the designer.
In the recent past, procedures have been developed and implemented, which make possible the creation of addendums in a more efficient manner. These are based on an addendum being described by means of flat sectional profiles. The known sectional profiles are different to link, resulting in bad interpolation data for addendum surfaces. For most tools, in addition, a limited number of such sectional profile types are sufficient. If one applies sufficient flat sectional profiles radially outwards from the component edge, then from it, by an interpolation transverse to the sectional profiles, the addendum surface can be more or less automatically created. In doing so, the indication of a few sectional profiles is sufficient to be able to then interpolate the sectional profiles from it. This method is not convincing. By a variation of the sectional profiles the addendum can be varied. With this procedure, the user, as compared to previous iterative methods, can save time in the development and modification of the addendum. The resulting addendum surfaces are still problematic due to insufficient results from interpolation. These procedures are stand alone solutions not linked with other devices, e.g. simulation modules.
This procedure, however, has the following serious disadvantages and problems. On the one hand, the smoothing of the edge of the component represents a major problem. The edge of the component geometry, where the addendum is to be applied, is in most instances not a smooth curve, but rather more frequently has sharp-angled indentations, tongues, etc. If now the same sectional profile throughout is applied to this edge, then these indentations, etc. continue into the addendum, which can lead to an extremely irregular addendum surface. In order to prevent this, the user once again is compelled to manually introduce many sectional profiles at the indentations and to adapt them such that they lead to a fairly smooth addendum surface. Alternatively, it is attempted to first fill up and to equalize the indentations, tongues, etc., with the help of traditional CAD functionality, so that a new, sufficiently large smooth component edge is produced, from which then the sectional profiles are applied. Both solutions require a lot of time and lead to the result that no usable addendum can be produced fully automatically. The latter fact is a disadvantage, particularly if one would like to automatically design, resp., optimize the addendum via an optimization loop in conjunction with a forming simulation code and a quality criterion. On the other hand, the sectional profile direction is difficult to determine automatically. The directions in which the sectional profiles are applied away from the component edge (resp., from the filled out component edge), decisively determine the generated addendum surfaces. In applying the directions vertical to the edge of the component projected in the drawing direction, at concave points overlaps of the sectional profiles result, which makes the creation of the addendum surface impossible.